Bicycle Generator Design

It sounds like you have got out all you can. Turning it faster won't help as you say it self limits, you can mess around and get either more volts or more amps, but not both at the same time. Sound like you need a different motor, a rewind or a purpose designed device.

The only bad thing is the 'limiting resistors' they are wasting power... have more leds in series and less resistance, or lower the output of the generator?
Del

Here is a suggestion for making more power available, that also could help in keeping weight low, streamlining and reducing load placed on cyclist.

Your current system self limits at walking speed. This suggests you are using the wheel to drive the generator. This seems to be the universal approach. Because bicycles travel at a wide range of velocities, much of the range is typically unoptimized.

Crank speed (pedal rate) has a smaller range than wheel speed. Drawing power at the crank not only provides a narrower range of RPM, but also has the advantage of being taken prior to the chain, gears and wheels. This means the power required to turn the generator does not first have to suffer losses from that portion of transmission and gearing.

The left side of the crankshaft and bottom bracket are typically relatively free workspace. The bottom bracket and crankshaft provide a solid interface with a low center of gravity that facilitates streamlining with the bike frame.

I would suggest keeping most of the system above the bottom bracket between the down tube and the seat tube.. safe from high centering below and safe from mud from the rear tire.... also easily streamlined.

Some of the new supercapacitors are really cheap and incredibly power dense....

B.B.B.

I don't understand that voltage self-limiting issue. It really shouldn't be there anywhere near mechanical limits of the stepper. R U sure it's not 5 wire unipolar motor? (windings having common pole?) If it is then slightly different rectification scheme is needed. Anyway switching DC/DC convertion is the way to go if U want more power as suggested by poster 1. Please give more info of your cirquit and motor so we're able to be of more help 53 2E 4D 2E

Yes, it is a 5 wire unipolar motor. It looks like I have chosen the wrong way to take off power. I assume I should have used a full-wave centre-tap rectifier setup??

I am looking at using an LM2575 regulator. This is a compromise between price and power handling.

Forgive me Phaddy, I am mechanical. I don't understand why you would want the baby generator to be self-limiting, is there some limit as to how fast the batteries can be charged?

Maybe it is just the way the little gizmo is made and it was available at the right price.

If that is the case why not just add another of them somewhere into the system. Perhaps on the opposite side of the tyre to balance out any side thrust or on the idler gear that is part of the chain guide.

BAB

The unit appears to be electrically self-limiting. I suspect the steel is not good enough at high frequency. At walking pace, 3 mph, frequency output is 88 Hz. At 20mph it will rise to 585 Hz.

It is handy to have it self-limit, the voltage is not excessive.

The friction from this little beast is remarkably little. You can spin the wheel by hand and it doesn't slow down the way the old 2/4 pole units used to. The poles are small and not too widely spaced, so there is just a slight judder as you turn the unit. The drive wheel on the motor is 2 inches diameter.

600 Hz is not a cut-off frequency even for the worse steel.Lower efficiency maby but not cut off. Possibly your diodes are too slow or connection problem. Didn't get answer about stepper type (wire number etc). Also test if winding resistances are concistent 53 2E 4D 2E